The present invention relates generally to methods and structures for sealing and, more particularly, a hybrid seal for sealing adjacent components of a turbine engine.
A number of applications have sealing arrangements between adjacent components. In some applications, seals enable relative motion between the adjacent components, while substantially minimizing fluid leakage between such components. These seals often vary in construction depending upon the environment, the fluids, the pressure ranges, and the temperature ranges.
For example, turbine engines generally have seals between stationary components, such as inner shrouds or outer shrouds. In these turbine engines, the inner shrouds are generally subjected to hot combustion gases, whereas the outer shrouds are subjected to cool purge gases used to cool outer and inner shrouds. It is therefore important to seal the inner and outer shrouds to prevent flows of the hot combustion gases into the outer shrouds and to prevent leakage of the cold purge gases into the inner shrouds. For example, leakage of the hot combustion gases into the outer shrouds could damage or adversely affect life of the turbine engine components.
Traditionally, the inner and outer shrouds are metallic. Therefore, existing seals include metal splines positioned against the inner shroud at locations of hot combustion gases, such that the splines reduce leakage of the hot combustion gases into the outer metallic components. Metal cloth seals also may be employed at such locations. In operation, these metallic seals may accommodate different thermal growths, non-uniformity or transient motion between adjacent components during operation of the turbine engine. Unfortunately, these metallic seals are prone to oxidation or chemical reaction by the hot combustion gases which limits their use as the operating temperatures in the turbine increase.
As a result, metallic sealing structures, such as metal splines and metal cloth seals, are not particularly well suited for higher operating temperatures. For example, higher temperature portions or stages of turbine engines may have temperature ranges approximately 100 to 200 degrees higher than current operating temperatures. Accordingly, higher temperature designs of turbine engines generally have inner shrouds made of materials suitable for these higher temperature ranges. For example, certain higher temperature turbine engines have inner shrouds made of a high temperature resistant ceramic material, such as a Ceramic Matrix Composite (CMC). The components surrounding the inner shroud, such as the outer shroud, are generally metallic in composition. Unfortunately, CMC components are difficult to machine, thereby making it difficult to mechanically capture the metallic seals in the locations of hot combustion gases. High-temperature interface seals, such as rope seals or ceramic block seals, are resistant to chemical reaction with the hot combustion gases, yet these seals do not provide the desired flexibility during periods of dissimilar thermal growth between the inner and outer shrouds.
In such applications as mentioned above, a spring-loaded seal may be employed to facilitate sealing of these CMC components. For example, a spring-loaded seal may have a rope seal with a central core of fibers, a surrounding resilient spring member supporting the core, and at least one layer of braided sheath fibers tightly packed together overlying the spring member. However, such a sealing mechanism, while having an improved resiliency and load bearing capacity, is likely to lose its resiliency when repeatedly loaded at high temperatures.
Therefore, a need exists for a system and method for effectively sealing components in applications, such as turbine engines.